The present invention relates to an electric conductometer, and an electrode for measuring electric conductivity and a method for producing the same, and specifically, relates to an apparatus capable of measuring electric conductivity accurately and stably, at a good repeatability substantially without requiring any cleaning of the electrode surface, and a method for producing the same.
Electric conductivity is especially employed as a scale to measure a concentration of ions capable of migrating in an aqueous solution, and an electric conductometer is employed to measure ion concentrations in many kinds of aqueous solutions. The electric conductometer has usually at least two electrodes, and the electric conductivity or resistance of an aqueous solution present between the electrodes is determined by measuring the electric current or voltage between at least two electrodes in contact with the aqueous solution.
The electrode of this electric conductometer is constructed usually from an oxidation and corrosion resistant conductive metal such as platinum black comprising fine particles of platinum, simply platinum, platinum or gold plated conductive metals, or stainless steel, in order not to be oxidized even when the electrode comes into contact with an aqueous solution, and in order to ensure stability of the measurement by setting an area of the electrode to be broad.
In such an electric conductometer, an electrode surface is usually cleaned regularly to perform an accurate measurement. Because many organic substances are generally contained in an aqueous solution to be measured, and are adhered or adsorbed onto an electrode surface, the adhered nonconductive organic substances heighten the resistance at the electrode surface, and the increase in the resistance may make an accurate measurement impossible, this electrode surface is regularly cleaned to avoid such inconvenience. Such adhesion or adsorption of organic substances has been considered to be an unavoidable phenomenon in a conventional apparatus, because of the measurement principle of an electric conductometer, that is, wherein ion exchange is performed on an electrode surface.
In other words, in a measurement of electric conductivity, because an electric current flows in a measurement system more or less, and the strength of the current is to be measured, a conductive electrode, namely, an electrode made from a conductive metal is inevitably used. Therefore, in an electrode surface made from a conductive metal, when ion exchange is performed by energization, nonconductive organic substances are adhered or adsorbed onto the electrode surface. When such adhesion or adsorption of the organic substances occurs, the resistance increases and an aimed electrode surface for measurement cannot be formed, and as a result, the measurement accuracy is sacrificed or a measurement repeatability is lost. Therefore, frequent cleanings of the electrode surface are required to avoid such an inconvenience.
Accordingly, it is an object of the present invention to provide an electric conductometer, which can automatically prevent organic substances contained in a measuring system from adhering or being adsorbed onto an electrode surface, and which can measure an electric conductivity stably and accurately at all times substantially without requiring any cleaning, and an electrode for measuring the electric conductivity and a method for producing the same.
To accomplish the above-described object, an electrode for measuring electric conductivity according to the present invention is characterized in that an electrode surface is formed by a titanium oxide layer on a surface of an electrode body made from a conductive metal.
Further, an electric conductometer according to the present invention comprises at least two electric conductivity measuring electrodes each body of which is made from a conductive metal and each surface of which is formed by a titanium oxide layer as an electrode surface, a space for storing a substance to be measured formed between the electrode surfaces of the electric conductivity measuring electrodes, and means for irradiating light to the electrode surfaces. A substance to be measured is generally an aqueous solution, but a gaseous substance or slurry-like substance can also be measured.
In this electric conductometer, it is preferred that light irradiated by the above-described means for irradiating light has a wavelength which brings about a photocatalyst activity of the above-described titanium oxide layer. For example, light with a wavelength from about 300 to about 400 nm can be employed. As means for irradiating light, a light source composed of means for irradiating ultraviolet rays and the like such as a black light may be directly employed, and a light guiding material (for example, an optical fiber or a tube and the like comprising a light guiding raw material) to guide light from a light source provided as means for irradiating light may be also employed. Further, the light from a light guiding material may be added to light irradiated directly from a light source.
Further, the above-described space for storing a substance to be measured may be defined by a light transmitting material, and it may be constituted so that the light from means for irradiating light is irradiated onto an electrode surface through the light transmitting material (for example, glass). In this case, if a titanium oxide coating layer capable of transmitting light is provided on a surface (a surface in contact with solution) of the side of the space for storing a substance to be measured (made of light transmitting material), adhesion of organic matters and the like to this surface of the light transmitting material can be prevented by super-hydrophilicity and decomposition property of organic substances ascribed to the titanium oxide layer.
Further, the aforementioned electric conductivity measuring electrode according to the present invention can be produced by the following method. Namely, a method for producing an electric conductivity measuring electrode according to the present invention is characterized in that an electrode surface is formed by providing a titanium oxide layer on a surface of an electrode body made from a conductive metal by sputtering or plating. Alternatively, a method can also be employed wherein an electrode surface made from a titanium oxide layer is formed by providing oxygen to a surface of an electrode body made from a titanium metal. As the method for forming a titanium oxide layer by providing oxygen, a method based on air oxidation other than a method utilizing electrolysis can be employed.
In the above-described electric conductivity measuring electrode and electric conductometer using the same according to the present invention, since the titanium oxide layer is formed on the surface of the electrode body made from a conductive metal, a photocatalyst activity of the titanium oxide is exhibited by irradiating light with an appropriate wavelength (for example, an ultraviolet ray) to the layer, organic substances in contact with the titanium oxide layer or existing nearby the layer in water are decomposed, and adhesion or adsorption thereof to the titanium oxide layer is automatically prevented. Therefore, it is not necessary to clean this electrode surface regularly, and the electrode surface is always maintained at a desirable surface condition without adhesion or adsorption of the organic substances, and an area of the electrode with such a desirable surface condition may be also maintained at an initial condition at all times. As a result, electric conductivity can be measured stably and accurately at all times, and repeatability of the accuracy of the measurement can be ensured with no problems.
Furthermore, according to the method for producing an electrode for measuring electric conductivity according to the present invention, the above-described electrode suitable for measurement of electric conductivity can be manufactured easily and inexpensively.